1. Field of the Invention
Illustrative embodiments of the present invention relate to an inkjet recording apparatus that ejects recording liquid onto a recording medium to form an image on the recording medium.
2. Description of the Background
Image forming apparatuses are used as printers, facsimile machines, copiers, multi-functional peripherals having two or more of the foregoing capabilities, or plotters. Such image forming apparatuses may include as an image forming section an inkjet recording device employing a liquid ejection method. The inkjet recording device ejects droplets of recording liquid, e.g., ink (hereinafter referred to as “ink droplets”), from nozzles of a recording head to form an image on a recording medium (sheet or material).
Such an inkjet recording device may include a maintenance unit that maintains good performance of the recording head. For example, a conventional type of maintenance unit includes a suction cap and a suction pump that suctions high-viscosity ink from the nozzles of the recording head covered with the suction cap. Such a conventional inkjet recording device may also include a supply pump that supplies ink from an ink cartridge to a recording head.
To perform cleaning to maintain good performance of the recording head, for example, a conventional type of inkjet recording device like that described in JP-3573059-B employs a so-called tube pump. The tube pump creates negative pressure in a capping unit that suctions ink from the recording head and supplies ink from a main tank to a sub tank through a tube. Such a tube pump has a relatively simple structure, allowing the device as a whole to be made more compact, and prevents ink contamination at a mechanical portion for suctioning and discharging ink. With such a configuration, in which ink is supplied from the main tank to the sub tank with the tube pump, while the pump is stopped, the tube is compressed in the tube pump to block a flow path and prevent ink from spontaneously flowing from the main tank to the sub tank by the negative pressure in the sub tank, thus maintaining pressure in the sub tank.
However, if the tube pump is left for a long time with the flow path of the tube blocked, compressed portions of the inner wall of the tube may stick together. Consequently, even if the pump is restarted to rotate, ink may not be supplied or suctioned. Usually, even if portions of the inner wall of the tube stick together, operating the tube pump pushes enough ink through the tube to resolve the blockage, thus allowing ink supply or suctioning to continue. However, at an approach to a compressed area of the tube, even if the pump is operated, ink may be not supplied to resolve the blockage in the tube, requiring waiting for spontaneously separation of the stuck portions of the inner wall. To prevent such a failure, it is conceivable that a sensor and a stepping motor might be used to prevent the pump from stopping at the approach to the compressed area of the tube. However, such a configuration may increase cost and size.